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Elliot the giant dinosaur, whose remains were discovered in the northern Australian state of Queensland a couple of years ago, could have died with a mate at its side, according to new fossil evidence.

Researchers led by Dr Steve Salisbury from the University of Queensland announced today that fossilised bones found in a dig near Winton, central-western Queensland, earlier this year have delivered what they think is a second dinosaur of the same species. They called their find Mary.

"It's still not clear what caused their deaths, but whatever happened, both carcasses ended up on the banks of a billabong or on the bend of a meandering river, somewhere in the middle of a vast, heavily forested coastal plain," Salisbury told ABC Science Online.

The researchers also found teeth from small therapods (medium sized meat-eating dinosaurs) and dwarf crocodiles with the dinosaur bones. The fact that these teeth are broken at their base suggested these other animals had been scavenging on the sauropod carcasses, Salisbury said.

Sauropods were giant plant-eating dinosaurs with a long neck and tail, and a relatively tiny head. Their legs were huge, with even the smallest ones having legs as thick as tree trunks. Better known sauropods include diplodocus, brachiosaurus and apatosaurus (previously known as brontosaurus).

The dig complements findings from earlier digs over the last couple of years that delivered the bones of Elliot, a 98-95 million-year-old sauropod, the largest dinosaur remains ever found in Australia. Elliot was named after the owner of the land where the fossils were found.

Salisbury had been mystified by the fact that many of Elliot's bones seemed to be too small to belong to him: "I was thinking this animal has got incredibly unusual proportions if they're the bones that I think they are," he said.

But during this year's dig, the discovery of several more bones helped solve the puzzle: "It's turned out that the majority of the bones that I initially thought belonged to Elliot actually belonged to this second, much smaller animal, which is called Mary."

Mary was named after palaeontologist Dr Mary Wade and is 10-12 metres long, half the size of Elliot. Salisbury said that if Mary was indeed a member of the same dinosaur species, she could be a juvenile. If not, it may be that females of the species were smaller than males. But the researchers do not have enough of the right bones yet to be 100% sure.

"So far we haven't found duplicate elements - the same bone that we can compare and say 'there we go, it's the same, and this one is bigger than other'. But from what we've got so far, they probably are the same species."

Salisbury hopes that next year's dig of what is now the ongoing Winton Dinosaur Project will settle this question. Although it might be harder to confirm what sex Elliot and Mary were since this would depend on finding a very particular bone in the dinosaur's tail: "It might be the other way around. It might be that Elliot is actually the 'she' and Mary is the 'he'," said Salisbury, adding they could even be the same sex.